1. Field of the Invention
The present invention relates to lamps and the heat absorption and transfer properties associated therewith. More particularly, the invention relates in one embodiment to improving the content of light usable in ultraviolet (“UV”) light curing applications along with improving the capture of unusable light and dissipating the heat associated therewith.
2. Description of the Related Art
The purpose of reflective surfaces in a UV curing system is to gather and direct the light emitted from a lamp (also referred to as a “light source”) directly to a two dimensional or three dimensional plane(s) or object(s) where UV curing will take place. In general, the mechanical structure that holds these reflective surfaces and the light source is called a housing. Some reflective surfaces discussed in detail herein are, in actuality, band-pass filters. These band-pass filters transmit certain wavelengths of light and reflect other wavelengths of light. Other reflective surfaces, referred to as “reflectors” reflect substantially all light incident thereon.
The light emitted from the light source is composed of three main regions of the electromagnetic spectrum: (a) wavelengths from about 200 nm to about 400 nm are generally considered to fall within the UV portion of the spectrum; (b) wavelengths from about 400 nm to about 760 nm are generally consider to fall within the visible part of the spectrum; and (c) wavelengths from about 760 nm to about 3,000 nm are generally considered to fall within the near infrared (“IR”) portion of the spectrum.
In conventional housings, the light is reflected by a planar reflector or mirror 16, as shown in FIG. 1. Inherent in this reflector design is the gathering and redirecting a part of the IR portion of the spectrum back across the surface of the lamp. This reflected IR light has been shown to cause unwanted radiant heat transfer back into the exterior and interior of the lamp. This additional heat can: (a) impair the efficient functioning of the lamp; (b) increase the operating temperature of the lamp; and (c) reduce the UV light output of the lamp.
One way to reduce the possibility of directing IR light back into the lamp is to remove the mirror 16 behind the lamp and to remove other reflective surfaces therearound that would otherwise redirect the IR light back into the lamp. However, as the mirror 16 and reflective surfaces redirect not only IR light but also UV and visible light, removing them to reduce the redirection of IR light would reduce the amount of UV light available in a UV curing application and decrease the overall efficiency of the system.
After the light is redirected in a second direction, it joins other light which originated on that second direction from the lamp; this combination of light must be separated into useable and unusable wavelengths. One way to separate the light is by using an optical filter such as a band-pass filter which may, for example, separate UV light from other types of light (e.g., IR and visible light) so that the UV light can be used in applications which depend on UV light (and which may be hampered by other types of light), such as UV curing applications.
Thus, the purpose of a band-pass filter in an optical system is to reflect light in a specific range of wavelengths and to transmit light of a different set of wavelengths. A particular type of band-pass filter, often referred to as a “cold mirror,” is used to provide good reflection of light having wavelengths in a particular range and to transmit light outside of that range. For example, one type of cold mirror reflects light having wavelengths between about 200 nm and about 450 nm (i.e., UV light and the lower end of the visible light spectrum) and transmits light having wavelengths above about 450 nm, i.e., light which includes most visible light and IR light.
Band-pass filters may be used to separate light into usable and unusable light. For example, a cold mirror may be used to separate light into UV light and visible/IR light. The UV light may be reflected toward a material, such as a web, that is to be cured via a curing application. By way of contrast, the visible/IR light may be transmitted through the cold mirror (i.e., it is not directed toward the curing application at hand), to prevent unnecessary and unwanted heating of the materials that are to be cured. A prior art embodiment incorporating a band-pass filter will be described with respect to FIG. 1.
FIG. 1 is a schematic view of a prior art lamp housing 100. The lamp housing 100 contains a lamp 26 (also called a “light source 26”) which projects diverging light having a variety of wavelengths from the interior 24 of the lamp 26. Some of the light is directed toward a reflective mirror 16 which reflects the light toward a band-pass filter 20, which may be a cold mirror. In some prior art embodiments, the mirror 16 is planar (as shown) whereas in other prior art embodiments the mirror 16 is curved. However, in all prior art embodiments, at least some of the light reflected by the mirror 16 is redirected back toward the light source 26.
Some of the light from the light source 26 is also reflected off shutters 12 toward the band-pass filter 20. The shutters 12, which rotate on axes 14, have inside surfaces (i.e., on the side facing the light source) which are highly polished. As a result, when an object 8 (which may be in the form of a tape or label) to be cured is moved across a window 22 in the housing 100, the shutters 12 may be opened and the polished surface of the shutters 12 used to gather and direct the light toward the band-pass filter 20.
The shutters 12 may be opened due to their being adapted to rotate on the axes 14. In a first position (not shown), the distal ends 13 of the shutters 12 approach each other, thereby substantially containing the light emitted by light source 26. In a second position, shown in FIG. 1, the distal ends 13 of the shutters 12 are separated so that the light emitted by the light source 26 can be reflected toward the band-pass filter 20.
The shutters 12 also serve a heat containment function. The temperature of the light source 26 may reach from about 650° C. to about 850° C. In some embodiments, as the light source 26 is reasonably close to the moving object 8, if the object 8 is stopped while the lamp housing 100 is emitting light, it may be preferable to protect the object 8 from the heat associated with the light emitted by light source 26 by closing the shutters 12.
The band-pass filter 20 is adapted to reflect light having a wavelength which falls within a specified range and to transmit light having wavelengths outside of that range. For example, in UV curing applications, if a cold mirror is used for the band-pass filter 20, it may reflect light having wavelengths between about 200 nm and about 450 nm (i.e., UV light coupled with the lower end of the visible light spectrum) and transmit light outside of this range including the remainder of the visible light and IR light. The light which is reflected by the cold mirror passes through a protective window 22 and may be used in applications calling for a particular type of light, e.g., UV light.
As the remaining light (e.g. visible/IR) is transmitted through the band-pass filter 20, it may be necessary to protect people and/or items which may be harmed by exposure to this light. To address this concern, the light which is transmitted through the band-pass filter 20 may pass through an air corridor 52 and into a solid heat sink 30 where it may be absorbed and converted into heat energy via radiant heat transfer.
Air, which is fed into the air corridor 52 via inlets 50, may be used to cool the heat sink 30. Similarly, air may be fed into the housing 100 via inlets 40. The air passing through the inlets 40 may be used to cool the light source 26, the mirror 16, and/or the shutters 12. Further, the heat sink 30 may be designed so that its shape and cross-sectional area will allow the heat absorbed therein to be transferred to a stream of cooling air in the air corridor 52 via forced/induced convection. Unfortunately, the heat sinks currently used tend to be large, expensive, and inefficient. Thus, although a solution, in the form of a heat sink apparatus, currently exists to absorb visible and infrared light transmitted through a band-pass filter, the solution is imperfect due to the size and cost of the heat sink apparatus.
In light of the aforementioned, it is desired to achieve one or more of the following in a new apparatus and method: (a) effectively redirecting light without unnecessarily heating of the lamp; (b) effectively absorbing visible/IR light; (c) dissipating the heat associated with the light absorption; and/or (d) reducing the size and/or cost of the current heat sinks used for this purpose.